Hydrophone module for a marine seismic cable

ABSTRACT

A low-profile hydrophone module for a marine seismic system includes a block having a curved surface and a receiving surface in which an open cavity is disposed, a hydrophone assembly, to which lead wires attach, disposed in the cavity, lead wires which pass out of the cavity, and a sound-transmitting material which fills the cavity. In another feature, the hydrophone assembly includes a hydrophone and a baffle material, the baffle material enclosing the hydrophone, the cavity is sealed around the lead wires, the sound-transmitting material is oil, and a cover sealingly affixes over the cavity. In another feature, the hydrophone assembly includes a hydrophone and a frame, the cavity is sealed around the lead wires, the sound-transmitting material is a potting sealant, and a cover sealingly affixes over the cavity.

BACKGROUND OF THE INVENTION

This invention relates to marine seismic cables, and, more particularly,to a towed seismic cable which flexible solid materials, disposed withinthe cable, buoyantly support.

For many years, the marine seismic exploration industry has relied onfluid-filled seismic cables. Marine seismic cables are one of the mostcritical components aboard today's seismic exploration vessels, and havea direct affect on the accuracy of the results which researchers andtechnicians obtain. The amount and type of fluid in oil-filled cablesmust be adjusted dependent on changes in water temperature and/orsalinity. Also, oil-filled cables are prone to leakage. The outer jacketof the seismic cables of the prior art is prone to rapture or tearing.This is particularly undesirable because this exposes the internalelectronic components to seawater, and disrupts the buoyancy of thecable.

Some of the hazards which seismic cables face include underwaterobstructions, fishing vessels, and sea animals. These hazards can severcables, which may then sink, and, consequently, cause significantdowntime and lost efficiencies.

U.S. Pat. Nos. 5,089,668, 5,141,796, and 5,471,436 disclose the use of abuoyant material to permit solid or semi-solid composition of a seismiccable. However, in these cases, the positioning or housing ofhydrophones is not discussed.

The industry needs a seismic cable which is streamlined, buoyant evenwhen the jacket ruptures, durable, and which requires littlemaintenance. The industry needs a seismic cable which requires lesschange-over time to accommodate different marine environments. Theindustry needs a seismic cable which minimizes hydrophone noisegenerated by the relative motion of cable components.

SUMMARY OF THE INVENTION

The present invention solves the foregoing problems, and achievestechnical advances, with a low-profile hydrophone module designed to beused with a solid marine seismic cable, or by itself, such as attachedto the outer surface of a ship. The low-profile hydrophone moduleincludes a block having a curved surface and a receiving surface inwhich an open cavity is disposed, a hydrophone assembly, to which leadwires attach, disposed in the cavity, lead wires which pass out of thecavity, and a sound-transmitted material which fills the cavity. Inanother feature, the hydrophone assembly includes a hydrophone and abaffle material, the baffle material enclosing the hydrophone, thecavity is sealed around the lead wires, the sound-transmitting materialis oil, and a cover sealingly affixes over the cavity. In anotherfeature, the hydrophone assembly includes a hydrophone and a frame, thecavity is sealed around the lead wires, the sound-transmitting materialis a potting sealant, and a cover sealingly affixes over the cavity.

An object of the invention is to provide a hydrophone module whichminimizes hydrophone noise generated by the relative motion of cablecomponents, thus improving reception.

Another object of the invention is to provide a low-profile hydrophonemodule which may be used separately from the hydrophone housings, suchas on the hull of a boat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general overall view of an illustrative seismic cableassembly towed behind a boat, the assembly containing many hydrophones.

FIG. 2 is an exploded view of the preferred embodiment of the solidmarine seismic cable assembly.

FIG. 3 is a cross-sectional view of the load-bearing fiber bundle of thepreferred embodiment.

FIG. 4 is a cross-sectional view of the cable of the preferredembodiment.

FIG. 5 is a perspective view of a hydrophone housing of the preferredembodiment.

FIG. 6a is a cross-sectional view of a hydrophone housing of thepreferred embodiment.

FIG. 6b is a cross-sectional view of a hydrophone cap of the preferredembodiment.

FIG. 6c is a plan view of the hydrophone cap of the preferredembodiment.

FIG. 7a is an exploded cross-sectional view of an alternate embodimentof the hydrophone cap.

FIG. 7b is plan view of the alternate embodiment of FIG. 7a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a boat 12 tows a solid marine seismic cableassembly 10. The cable assembly 10 contains hydrophones 14 (shown inFIG. 6).

Referring to FIG. 2, the cable assembly 10 includes a cable 16,hydrophone housings 20, a buoyant filler 24, and an outer protectivejacket 28. The cable 16 includes a load-beg fiber bundle 32,data-transmitting wires 36, power conductors 38, and optical fibers 40encased in stainless steel tubes, and a clear, protective sheath 42. Theoptical fibers 40 transmit telemetry data.

Referring to FIG. 3, the load-baring fiber bundle 32 includes a thincover 46 enclosing a counter-helix-wrapped high-strength fiber 52. Thecover 46 protects the fiber 52 from abrasion by the data-transmittingwires 36, power conductors 38, and optical fibers 40 (shown in FIG. 4).The fiber 52 is "KEVLAR 29", available from E. I. Du Pont, located inWilmington, Del. Referring to FIG. 4, the data-transmitting wires 36,power conductors 38, and optical fibers 40 surround the load-bearingfiber bundle 32. The protective sheath 42 surrounds the assembly ofthese four items.

Referring again to FIG. 2, the hydrophone housings 20 clamp around thecable 16, in a spaced-apart relationship. Each hydrophone housing 20including a hydrophone module or hydrophone cap 56, and each hydrophonecap contains a hydrophone 14 (as shown in FIGS. 6 and 7). The buoyantfiller 24 surrounds the cable 16 between the hydrophone housings 20.

The outer protective jacket 28 surrounds the hydrophone housings 20 andthe buoyant filler 24. The protective jacket 28 is a composite jackethaving an internal layer 62 of polyurethane and an external layer 66 ofpolyvinyl chloride. The protective jacket 28 is available from BaylandCorporation of Gavel, Tex., in a co-extruded form. The protective jacket28 seals the cable assembly 10 from water.

The buoyant filler 24 is a split tube which is a composite mixture ofthermoplastic elastomer and glass microspheres, the composite mixturehaving a specific gravity of from 0.76 to 0.82. The elastomer is"VISTA-FLEX", Part No. 9601-74, available from Advanced Elastomers, Inc.of Akron, Ohio. The glass microspheres are "SCOTCHLITE" brand, Part No.B381/4000, available from 3M Corporation of St. Paul, Minn. The buoyantfiller 24 substantially films regions being bounded by an outermostcylindrical surface 70 of the table 16 and an imaginary cylindricalsurface, which extends between outermost cylindrical surfaces 74 ofadjacent hydrophone housings 20. An adhesive (not shown) applied along asplit in the split tube bonds the buoyant filler 24 around the cable 16.

Each hydrophone housing 20 further includes a top portion or top mount78 and a bottom portion or bottom mount 82. Each mount 78 and 82 has awire-clearance recess 90. Each mount 78 has a receiving recess 86, andthe mount 82 may optionally have a receiving recess 86. The mounts 78and 82 each include a contact surface 94 which contacts the cable 16when the mounts fasten around the cable. The contact surface 94 includesraised ribs or bosses 98 (most clearly shown in FIG. 6). The mounts 78and 82 clamp around the cable 16 via screws 102. The bosses 98 securelygrip the cable 16 by increasing contact pressure per unit area betweenthe bosses and the cable.

The hydrophone housing 20 is fabricated from a high strength, lightweight, rigid, injection-moldable, composite polymer of about 40% byweight glass fiber fill in a polyurethane resin. Suitable polymersinclude "ISOPLAST", Part. No. 800-441-4DOW, available from DOW ChemicalCompany of Midland, Mich., or "ESTALOC", available from B. F. GoodrichCorporation of Jacksonville, Fla.

Referring to FIG. 6a, the mounts 78 and 82 further include a wirepassageway 106 between the receiving recess 86 and the wireclearancerecess 90. Referring now to FIGS. 6b and 6c, the hydrophone cap 56includes a block 110 and an isolator 112. The block 110 has an outercurved or cylindrical surface 118 (as shown in FIGS. 2 and 5), endsurfaces 122 and 126, and a receiving surface 130. The receiving surface130 intersects the cylindrical surface 118. The block 110 has a cavity134. The cavity 134 has a perimetrical edge 142 which the intersectionof the cavity and the receiving surface 130 defines.

A hydrophone assembly 150 installs in the cavity 134. The hydrophoneassembly 150 includes a hydrophone 14, lead wires 154, and a hydrophoneframe 158. The hydrophone is a "PRESEIS" brand hydrophone, availablefrom Input/Output, Inc., of Alvin, Tex. The hydrophone 14 mounts in thehydrophone frame 158. The hydrophone frame 158 supports the hydrophone14 within the cavity 134.

Lead wires 154 electrically connect to the hydrophone 14. The lead wires154 pass through apertures 166 to the exterior of the hydrophone cap 56.A sealant (not shown) seals the apertures 166.

The hydrophone 14 is potted in the cavity 134 with a potting sealant135. The preferred potting sealant is "POLYSET", Part No. PC3062,available from Polyset Company in Mechanicville, N.Y. The pottingsealant 135 fills substantially all the space in the cavity 134 notoccupied by the hydrophone 14. An isolator 112 fits between the cap 56and the receiving recess 86, and is sealed to the filled cavity 134 andthe receiving recess 86 with a gasket compound such as "PERMATEX",available from Permatex Industrial Division, Rock Hill, Conn., in orderto eliminate any voids between the isolator 112 and the potting sealant135 and the receiving recess 86.

Referring to FIGS. 5 and 6a, screws 168 capture the isolator 112 uponassembly of the cap 56 to the receiving recess 86 (depicted in FIG. 1)on the mounts 78 or 82. The screws 168 pass through the hydrophone cap56 and the isolator 112, into the mounts 78 or 82. The isolator 112 isrigid and has a high Modulus of Elasticity. The isolator 112 ispreferably made from a 0.035 inch thick series 300 stainless steelplate.

The lead wires 154 connect to the appropriate data-transmitting wires 36of the cable 16, via splices (not shown). The wire-clearance recess 90contains the splices. The outer cylindrical surface 118 of eachhydrophone cap 56 is flush with an outer cylindrical surface 178 of eachhydrophone housing 20. The hydrophone mounts may use a single hydrophoneas shown in FIG. 5, or may support two hydrophones, as shown in FIG. 6a,or more, as desired.

Referring now to FIGS. 7a and 7b, in an alternate embodiment thehydrophone cap 56 includes a block 108 and a cover 114. The block 108has an outer curved or cylindrical surface 118 (as shown in FIGS. 2 and5), end surfaces 122 and 126, and a receiving surface 130. The receivingsurface 130 intersects the cylindrical surface 118. The block 108 has acavity 136 and a gasket-receiving channel 168. The cavity 136 has aperimetrical edge 142 which the intersection of the cavity and areceiving surface 130 defines. The channel 138 circumscribes theperimetrical edge 142. The channel 138 contains a gasket 146.

A hydrophone assembly 152 installs in the cavity 136. The hydrophoneassembly 152 includes a hydrophone 14, lead wires 154, and a bafflematerial 162. The baffle material 162 positions the hydrophone 14centrally in the cavity 136. The baffle material 162 is an open cellfoam structure.

Lead wires 154 electrically connect to the hydrophone 14. The lead wires154 pass through apertures 166 to the exterior of the hydrophone cap 56.A sealant (not shown) seals the apertures 166. An oil 170 fills thecavity 134 and immerses the hydrophone assembly 152. The oil 170 is aliquid which is acoustically transparent and which has a density similarto that of water. Suitable oils include castor oil, "ISOPAR H",available from Exxon Corporation of Houston, Tex., and "PARATHERM NF",available from Paratherm Corporation of Conshohocken, Pa. The cover 114sealingly fits over the cavity 134 and the channel 138. The cover 114 isrigid and has a high Modulus of Elasticity. The cover 114 is preferablymade from a 0.035 inch thick series 300 stainless steel plate. Pan-headfasteners 174 securely attach the cover 114 to the block 108.

Referring to FIGS. 5 and 6, the hydrophone cap 56 installs in thereceiving recess 86 (depicted in FIG. 1) of the mounts 78 and 82. Thescrews 168 fasten the hydrophone cap 56 to the mounts 78 and 82. Thelead wires 154 connect to the appropriate data-transmitting wires 36 ofthe cable 16, via splices (not shown). The wire-clearance recess 90contains the splices. The outer cylindrical surface 118 of eachhydrophone cap 56 is flush with an outer cylindrical surface 178 ofhydrophone housing 20.

Referring again to FIG. 2, a method of making the marine seismic cable10 includes the following steps: surrounding the load-bearing fiberbundle 32 with data-transmitting wires 36, power conductors 38, andoptical fibers 40 (shown in FIG. 4); enclosing the load-bearing fiberbundle 32, the data-transmitting wires 36, the power conductors 38, andthe optical fibers 40 with the protective sheath 42; clamping hydrophonehousings 20 along the cable 16; electrically connecting the hydrophone14 in each hydrophone housing 20 to the appropriate data-transmittingwires 36, via a splice; installing the tubular, buoyant filler 24between the hydrophone housings 20 and around the cable 16; andenclosing the cable 16, the hydrophone housing 20, and the buoyantfiller 24 with the protective jacket 28.

Referring again to FIGS. 6a, 6b, and 6c, a method of the hydrophone cap56 for the cable assembly 10 includes the following steps: forming theblock 110 having the cylindrical surface 118 and the cavity 134, whichis disposed in the receiving surface 130 of the block 110; mounting thehydrophone 14, to which lead wires 154 attach, in the hydrophone frame158, thus creating the hydrophone assembly 150; install the hydrophoneassembly 150 in the cavity 134; passing the lead wires 154 out of thecavity 134; sealing the cavity 134 around the lead wires 154; pottingthe hydrophone assembly 150 in the cavity 134 with potting sealant 135;and sealingly mounting the isolator 112 to the potted assembly and thereceiving recess 86, using a gasket compound such as "PERMATEX".

Referring again to FIGS. 7a and 7b, an alternate method of making thealternate embodiment of the hydrophone cap 56 for the cable assembly 10includes the following steps: forming the block 108 having thecylindrical surface 118 and the cavity 136, which is disposed in thereceiving surface 130 of the block 110; mounting the hydrophone 14, towhich lead wires 154 attach, in the baffle material 162, thus creatingthe hydrophone assembly 152; installing the hydrophone assembly 152 inthe cavity 136; passing the lead wires 154 out of the cavity 136;sealing the cavity 136 around the lead wires 154; and mounting the cover114 over the cavity 136.

In operation, the cable assembly 10 connects to a data recording unit(not shown) on board the boat 12. The cable assembly 10 unwinds from aspool (not shown) on the boat 12, and lowers into the water. Thehydrophone 14 receives acoustic waves which pass through the protectivejacket 28, the outer cylindrical surface 118 of the hydrophone cap 56,and the potting sealant 185 or the oil 170. The hydrophone transducesthese acoustic waves into electrical signals which transmit through thelead wires 154, the splice, and the data-transmitting wires 36, tostreamer electronic modules (not shown), which then send the data viatelemetry over the optical fibers 40 to the data recording unit on theboat 12.

An advantage is that for a solid cable, the protective jacket 28 iscontinuous along the length of the cable assembly 10, thus making thecable assembly streamlined. This minimizes noise by minimizing unevensurfaces which disrupt laminar flow around the cable assembly 10.

Another advantage is that the cable assembly 10 is buoyant even when theprotective jacket 28 ruptures.

Another advantage is that the cable assembly 10 is durable, and requireslittle maintenance.

Another advantage is that the cable assembly 10 requires lesschange-over time to accommodate different marine environments becausethe buoyancy of the solid-filled cable is less affected by watertemperature, as compared to a fluid-filled cable.

Another advantage of the invention is a hydrophone module whichminimizes hydrophone noise generated by the relative motion of cablecomponents, thus improving reception.

Another advantage is that the isolator 112 significantly improves thesensitivity of the hydrophone 14. The isolator 112 also compensates fora thin wall between the receiving recess 86 and the contact surface 94.In addition, the isolator 112 may reduce noise originating from withinthe cable 16 or inside the cable assembly 10.

Another advantage is that the baffle material 162 isolates thehydrophone 14 from the block 110 and the cover 114.

Another advantage is that, due to its thin profile, the hydrophone cap56 may be used separately from the hydrophone housing 20, such as on thehull of the boat 12.

In an alternate embodiment, the baffle material 162 retains thehydrophone 14 against relative motion within the cavity 134, eliminatingthe need for the hydrophone frame 158.

In another alternate embodiment, as depicted in FIG. 4, a method ofmaking the solid marine seismic cable assembly 10 includes the steps of:surrounding the load-bearing fiber bundle 32 with the data-transmittingwires 36, the power conductors 38, and the optical fibers 40; enclosingthe load-bearing fiber bundle 32, the data-transmitting wires 36, thepower conductors 38, and the optical fibers 40 with the protectivesheath 42; clamping the hydrophone housings 20 along the cable 16;installing the buoyant filler 24 between the hydrophone housings 20 andaround the cable 16; electrically connecting the hydrophone 14, in eachhydrophone housing 20, to the appropriate data-transmitting wires 36;and enclosing the cable 16, the hydrophone housings 20, and the buoyantfiller 24 within the protective jacket 28.

In another alternate embodiment, the receiving recess 86 on the mounts78 and 82 is elongated along the longitudinal as of the housing 20, soas to accommodate two hydrophone caps 56. The lead wires 154 from thetwo hydrophone caps 56 share a common wire-clearance recess 90 and awire passageway 106.

In another alternate embodiment, the buoyant filler 24 fastens aroundthe cable 16 with a mechanical fastener (not shown).

Although an illustrative embodiment of the invention has been shown anddescribed, other modifications, changes and substitutions are intendedin the foregoing disclosure. Accordingly, it is appropriate that theappended claims be construed broadly and consistent with the scope ofthe invention.

What is claimed is:
 1. A low-profile hydrophone module for a marineseismic system containing data-transmitting wires, the hydrophone modulecomprising:a. a block having a curved surface and a receiving surface inwhich an open cavity is disposed; b. a hydrophone assembly, to whichlead wires attach, disposed in the cavity; c. lead wires which pass outof the cavity; d. a sound-transmitting material which fills the cavity:and e. a wire-clearance recess disposed in the receiving surface, thewire-clearance recess displaced from the open cavity along alongitudinal axis of the block, the wire-clearance recess of sufficientsize to receive connections between the lead wires and thedata-transmitting wires.
 2. The hydrophone module of claim 1, whereinthe hydrophone assembly comprises a hydrophone and an open cell foambaffle material, the baffle material enclosing the hydrophone, thecavity is sealed around the lead wires, the sound-transmitting materialis oil, and a cover sealingly affixes over the cavity.
 3. The hydrophonemodule of claim 1, wherein the hydrophone assembly comprises ahydrophone and a frame, the cavity is sealed around the lead wires, thesound-transmitting material is a potting sealant, and a cover sealinglyaffixes over the cavity.
 4. The hydrophone module of claim 2, whereinthe curved surface is a cylindrical surface, and wherein the block hasend portions and a receiving surface through which the hydrophoneassembly installs in the cavity.
 5. The hydrophone module of claim 3,wherein the curved surface is a cylindrical surface, and wherein theblock has end portions and a receiving surface through which thehydrophone assembly installs in the cavity.
 6. The hydrophone module ofclaim 4, wherein the baffle material positions the hydrophone centrallyin tie cavity.
 7. The hydrophone module of claim 5, wherein thehydrophone frame supports the hydrophone within the cavity.
 8. A methodof making a hydrophone module for a marine seismic system containingdata-transmitting wires, the steps comprising:a. forming a block havinga curved surface and a receiving surface in which an open cavity and awire-clearance recess are disposed, the wire-clearance recess displacedfrom the open cavity along a longitudinal axis of the block; b.installing a hydrophone assembly, to which lead wires attach, in thecavity; c. passing the lead wires out of the cavity; and d. filling thecavity with a sound-transmitting material, wherein the wire-clearancerecess is of sufficient size to receive connections between the leadwires and the data-transmitting wires.
 9. The method of claim 8, whereinthe sound transmitting material is a potting sealant.
 10. The method ofclaim 9, wherein the hydrophone assembly comprises a hydrophone mountedwithin a hydrophone frame, and, prior to the filling of the cavity, thecavity is sealed around the lead wires, and, after the filling, a coversealingly affixes over the cavity.
 11. The method of claim 10, whereinthe curved surface is a cylindrical surface, and wherein the block hasend portions and a receiving surface through which the hydrophoneassembly installs in the cavity.
 12. The method of claim 8, wherein thesound transmitting material is an oil.
 13. The method of claim 12,wherein the hydrophone assembly comprises a hydrophone enclosed within abaffle material, and, prior to the filling of the cavity, the cavity issealed around the lead wires, and, after the filling, a cover sealinglyaffixes over the cavity.
 14. The method of claim 13, wherein the curvedsurface is a cylindrical surface, and wherein the block has end portionsand a receiving surface through which the hydrophone assembly installsin the cavity.